Inkjet printing processes can include the use of a liquid ink jetted from a printhead through a plurality of nozzles. The ink can be jetted directly onto a print medium such as paper, plastic, or textile. In an aqueous transfix process, a water-based ink can be jetted directly onto a surface of an intermediate transfer member such as a rotating belt or drum, or onto a sacrificial coating, such as a polyurethane coating, applied to the intermediate transfer member. After the ink is jetted, the ink is transferred through pressure from a pressure roll, and physical contact between the ink and the print medium at a transfix nip, from the surface of the intermediate transfer member to a surface of the print medium.
While jetting of the ink onto the intermediate transfer member typically occurs at a jetting viscosity, a better transfer of the ink from the intermediate transfer member to the print medium may be realized if the ink viscosity at the point of transfer is higher than the jetting viscosity. Thus a printer employing an aqueous transfix process typically includes infrared heaters to heat the ink after the ink is jetted onto the intermediate transfer member but before it is transferred to the print medium to remove a desired amount of solvent (i.e., water) from the ink. While some drying is preferred, the heating is carefully controlled to ensure that the ink is not excessively dried, which would degrade the transfer of the ink to, and bonding of the ink with, the print medium.
The surface of the intermediate transfer member should have various physical, chemical, and thermal properties so that the ink is properly transferred to the print medium. The intermediate transfer member is typically designed so that its outer surface retains as much of the thermal energy output from the heaters as possible to improve control of the ink viscosity. If heat is transferred deeper to the inner layers of the intermediate transfer belt, viscosity control of the ink becomes more challenging, for example because it becomes more difficult to estimate the amount of heat transferred to the ink, and thus the amount the ink is dried, compared to the amount of heat retained by the intermediate transfer member. Ideally, thermal energy from the printer heaters would be retained only in the outer surface of the intermediate transfer member.
Further, the surface energy of the intermediate transfer member should be sufficient to reduce the spread of ink across the intermediate transfer member before it is transferred to the print medium. The surface of the intermediate transfer member should also be flexible, non-compressible, and sufficient to release the ink to the print medium at the transfix nip.
An intermediate transfer member can include a silicone layer outer surface or “transfix blanket” that is adhered to a stainless steel substrate with an adhesive. The stainless steel substrate can, in turn, be wrapped around an aluminum drum. The silicone layer outer surface can optionally include fillers in an attempt to improve heat retention for ink drying and surface energy for ink release and transfer. The intermediate transfer member may also include a foam layer underlying the silicone layer to provide a thermal insulation layer to reduce heat transfer to the underlying stainless steel layer. While the foam layer may improve thermal properties of the intermediate transfer member, it may also increase compressibility of the silicone surface during contact with the pressure roll at the transfix nip, which is typically to be avoided.
An intermediate transfer member design having an improved heat retention at the outer surface and which is sufficiently non-compressible would be desirable.